Electrical motors are in vast use and impact every aspect of industrial, commercial and residential life. Such motors can vary from small, fractional motors that can be found, for example in washing machines and refrigerators, to large industrial applications for driving manufacturing equipment, fans and the like. Motors are commonly used to convert electrical energy into rotating energy or rotational force.
Typically, a motor includes a rotating central portion referred to as a rotor and a stationary outer portion referred to as a stator. The stator and rotor are housed in a housing that contains the motor. Both the rotor and stator contain electrical conducting elements. Rotor and stator cores can be formed with varying numbers of slots, which are the openings that receive the electrical conducting elements.
A rotor core is the central portion of the rotor that contains the conductive elements. The number of bars in rotor cores can vary considerably. In smaller, fractional squirrel-cage motors, for example, those having rotor diameters of about 2 inches, the number of bars is generally between 8 and 52. The core structure is typically formed as a plurality of stacked plates or laminations. The laminations, which can be metal, may be punched in a press, and subsequently stacked one on top of another to form the core. Because of the possible asymmetries in the lamination material, the laminations can be rotated so that the core, upon final assembly, forms a straight, rather than lopsided, stack. The laminations are interlocked with one another to form a rigid core structure, and to prevent the laminations from shifting relative to one another. Stator cores are formed in a like manner.
In one known interlocking arrangement, each lamination has a dimple or a recess punched into the surface, which forms a corresponding projection on the opposite side of the lamination. The laminations are then stacked one on top of the other with the projections from one lamination engaging and resting in the recess in the next adjacent lamination. In this nested arrangement, the laminations are kept in alignment with one another by engagement of the projections and recesses. This is a common and accepted method for interlocking laminations.
Although such known methods are in common practice, they do have their drawbacks. First, there is a mathematical dependency between the number of slots in the rotor or stator and the number of interlocks. Typically, the number of rotor slots and the number of interlocks are chosen such that they are both divisible by 3, 4 or 5, to yield rotations of 120, 90, and 72.5 degrees, respectively. Although this may be adequate when the rotor or stator has a quantity of slots that is readily divisible by such numbers, it is unacceptable when the number of slots in the rotor varies from such readily divisible numbers. For example, when the number of slots is 12, 15, 16, 20, 24, 28, 30, 32, 36, 40, 42, 45 or 48, the number of interlocks can be sufficient (e.g., between 3 and 4), and the rotational angles are readily determined by dividing the number of interlocks into 360 degrees.
As an example, a rotor having 12 slots can include 2, 3 or 6 interlocks, and will have rotational angles of 180, 120 and 60 degrees, respectively. It will however be readily apparent that when the number of bars varies from these readily divisible numbers, the incorporation of interlocks into a rotated core can become quite complex if not impossible. It follows that rotors having, for example, a prime number of bars (e.g., 13, 17, 19, 23, 29, 31, 37, 41, 43 or 47 bars) cannot be manufactured using the known method for interlocking laminations.
Moreover, it has been observed that rotor and stator cores having laminations having a quantity of slots that can only be rotated 180 degrees can be susceptible to forming a lopsided stack or core. That is, cores that include laminations that are rotated 180 degrees only, can produce an undesirable ovality in the finished core if an offset exists in punched holes that are intended to be concentric with one another.
Accordingly, there continues to be a need for a rotor and stator core lamination interlocking arrangement that is independent of the number of slots, which configuration accommodates lamination rotations, and further accommodates skewing of rotor core laminations relative to one another.
Additionally, there continues to be a need for a method for making such rotor and stator core laminations, which method does not increase, or preferably reduces the number of steps required in forming the core.